title: The effect of ketamine on human somatosensory evoked potentials and its modification by nitrous oxide.
abstract: The effect of ketamine alone and in combination with N2O (70% inspired) on median nerve somatosensory evoked potentials (SSEPs) was investigated in 16 neurologically normal patients undergoing elective abdominopelvic procedures. The anesthetic regimen consisted of ketamine (2 mg/kg iv bolus followed by continuous infusion at a rate of 30 micrograms.kg-1.min-1) [corrected], neuromuscular blockade (atracurium), and mechanical ventilation with 100% oxygen. SSEP recordings were obtained immediately preinduction and at 2, 5, 10, 15, 20, and 30 min postinduction. Thereafter, N2O was added with surgical incision and maintained for 15 min. At 5-min intervals, SSEP recordings were again taken during and after N2O. With minor exceptions, mean cortical and noncortical latencies as well as noncortical-evoked potential amplitude were unaffected by either ketamine or N2O. Ketamine induction increased cortical amplitude significantly with maximal increases occurring within 2-10 min. For example, at 5-min postinduction, mean N1-P1 amplitude increased from 2.58 +/- 1.05 (baseline) to 2.98 +/- 1.20 microV and P1-N2 amplitude increased from 2.12 +/- 1.50 (baseline) to 3.99 +/- 1.76 microV. Throughout the 30-min period after ketamine induction, mean P1-N2 amplitude increased generally by more (57-88%) than did mean N1-P1 amplitude (6-16%). N2O added to the background ketamine anesthetic produced a rapid and consistent reduction in both N1-P1 and P1-N2 amplitude. Thus, at 1 min after N2O, mean N1-P1 amplitude decreased from 2.74 +/- 1.11 to 1.64 +/- 0.63 microV, while P1-N2 amplitude decreased from 3.32 +/- 1.52 to 1.84 +/- 0.87 microV.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Anesthesiology, Cleveland Clinic Foundation, Ohio 44195-5154.
authors.forename: A
authors.initials: A
authors.lastname: Schubert
authors.forename: M G
authors.initials: MG
authors.lastname: Licina
authors.forename: P J
authors.initials: PJ
authors.lastname: Lineberry
mesh_terms: D000328:Adult; D000769:Anesthesia, Inhalation; D000771:Anesthesia, Intravenous; D004347:Drug Interactions; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects*; D006801:Humans; D007649:Ketamine / Q000494:pharmacology*; D008475:Median Nerve / Q000187:drug effects / Q000502:physiology; D008991:Monitoring, Physiologic; D009609:Nitrous Oxide / Q000494:pharmacology*
chemical_list: D007649:Ketamine; D009609:Nitrous Oxide